Covering the lowlands of the Caribbean, mainly in elevations below 500m above sea level, from southern Nicaragua, including northern Costa Rica and most of the Panamanian Caribbean, wet forests represent the epitome of humid and tropical forest. This forest ecoregion evolved from unique combinations of North American and South American flora and fauna, which met with the union of these continents 3 million years ago (Rich and Rich 1983). The resulting mixture has produced one of the richest and most diverse associations of plants and animals of any area of comparable size (Raven 1985). At present, a large part of this ecoregion has become subsistence and commercial agriculture.
Location and General Description
This ecoregion located in Central America has an environment charged with constant humidity and precipitation (DeVries 1987). Rainfall ranges from 2,500 mm in central Panama (Ridgely 1976) to more than 5,000 mm in southern Nicaragua.
Until recent geological times, the isthmus south of central Nicaragua was discontinuous, volcanically active, topographically and environmentally diverse. The basalt bed is the primary material of the residual and often unconsolidated soils that cover the mountainous areas of this ecoregion. The old alluvial terraces form the base of the swamp forests and the flat lands in the lower elevations and near the Caribbean coast (Hartshorn 1983; Vásquez Morera 1983). The northern section is formed by a broad relatively flat alluvial plain, with a gradual elevation change from sea level to 500 m, while to the south in Panama, steep slopes rise from the Atlantic Ocean, significantly reducing the ecoregion only 5-10 km wide.
It is characterized by an exuberant forest of perennial trees, that are large and have with canopies, which reach 40 m in height and an extremely rich epiphytic flora. The palm component includes many sub-canopy and understory species. Abundant species of palm trees such as Welfia georgii, Socratea durissima, Iriatea gigantea and in permanently flooded areas Raphia taedigera (Hartshorn 1983). Seasonal swamp forests occur in the lower and rim areas of Nicaragua and northern Costa Rica, particularly along the coast where they are classified in mangrove forests. In these forests, the Sparrowhawk (Pentaclethra macroloba) dominates the canopy, along with the caobilla (Carapa nicaraguensis). The almond tree (Dipteryx panamensis) and the monkey pot tree (Lecythis ampla) are two outstanding species that are rapidly disappearing and are regionally endemic to the lowlands, below 250 m above sea level.
In this area of abrupt and very humid topography, it rains more than 3,500 mm per year and there is no defined dry season. The temperature remains constant around 25 ° C, with possibilities of rain throughout the year, especially in the afternoons. As a result of the high rainfall, the area is crossed by infinity of very stony rivers that are fast and with waterfalls, where some reach several tens of meters of height.
Although biologically it is very diverse, this ecoregion has low levels of endemism. The high species richness is derived in large part from the mixture of flora and fauna of the North and South America, thanks to this land bridge (Rich and Rich 1983, Raven 1985). The resident fauna, including the taxa of butterflies, reptiles, amphibians, birds and mammals, are, for the most part, species representative of the humid tropical forest that extends from southern Mexico to northern South America (DeVries 1987; Stiles 1985). Wilson 1990; Guyer 1990). Endemic endemism among fauna is almost non-existent: between 80-100% of the mammal species that breed in northern Costa Rica also occur in Panama, Nicaragua, Honduras and Colombia (Stiles 1985, Wilson 1990). However, a series of birds of restricted distribution are shared with the humid forests of the Central American Atlantic, forming a zone of endemic birds together (Stattersfield et al 1999). The Caribbean side is an important migratory route (Stiles 1983); Neotropical and altitudinal migrants comprise about 30% of the avifauna, particularly in the foothills (adapted from Stiles 1985 and 1989).
Some large expanses of primary rainforest remain intact, present only in large reserves, particularly the Indio – Maíz (approximately 400,000 ha) biological reserve along the Nicaraguan coast (Cardenal Sevilla 1990) and in eastern Panama as length of La Amistad International Park. These blocks conserve almost all vertebrate species, including most large predators, although increasing isolation threatens their long-term viability (Powell pers communications, Stiles 1985). Although small in size, the La Selva Biological Station with 1,700 ha in northeastern Costa Rica hosts permanent populations of large predators (Panthera onca) and herbivores such as (Tapirus bairdii) probably because of its connection with the montane-high forests of Braulio National Park Cheek. In fact, this connection represents the last intact gradient of primary forest from sea level close to 2,900 m in Central America. (Lieberman et al., 1996). The Tortuguero National Park, along the Caribbean coast of northern Costa Rica, acts as an isolated refuge for many species, as does the Colorado Bar wildlife refuge – although the application of protection remains a challenge for both areas.
The forests are evergreen, of several strata, very dense and of great biological complexity. Due to environmental factors such as soil, slopes, drainage and wind exposure, several habitats have been developed that show marked differences in the height of the trees and the composition of the forest. The elevation of the forest mass varies, although, in general, it is quite high. Most trees in the upper stratum have more than 30 meters and emergent trees can reach more than 50 meters.
Some common species are the male cedar, the hawk, the maria, the ceiba, the javillo, the guayabón, the pylon, the naked Indian and the milky. Most of the trees are covered by a layer of mosses and lichens and in the branches proliferate orchids and other types of epiphytic plants. In the undergrowth, arborescent ferns abound and selaginella Selaginella sp.
The fauna is rich and varied, although the majority of the species, due to living in the canopies or because they are nocturnal, are rarely visible.
The Hitoy Cerere Biological Reserve, located 3 kilometers away, houses some 40 species of mammals, including some in danger of extinction. Among them are the ocelot, the ceibite, the tapir, the jaguar and the saino. The most easily observed are the tepezcuintles, the guatuzas, the rabbits, raccoons, coatis, squirrels, the three-toed sloth, the ceibite or the banana seraph, the four-eyed fox, the otter, the balsa fox, the mountain goat , the tolomuco, the tigrillo, and the congo and carablanca monkeys. More than 230 bird species have been observed in the area, including the Montezuma oriole, which congregates to build a large number of hanging nests in a single tree; the vulture, the blue-headed parrot, the booby chizo, the oropopo, the bluethroat hummingbird, the colloquial trogon, the green kingfisher and the black curré. Some such as the eared owl, the black hawk and the basket bird have small populations. Others such as the flycatcher, the orioles and the kingfishers, the sergeant, the toucans and the guans are commonly seen during walks along the trails and in the river. It is also common to see frogs inhabitants of the litter, chirbalas, Galicians, cherepo and snakes, both poisonous and harmless. Some 30 species of amphibians and 30 species of reptiles are known. Inside the invertebrates there are bullet and zompopa ants, colorful butterflies like those of the genus Morpho, huge dragonflies, bees and metallic colored drones. As for the plant species, about 380 are known. The forests are always green and very dense.
Although there are still some large blocks of intact habitat, the vast lowland forests of the Caribbean have been severely fragmented in recent years (Sánchez-Azofeifa et al., 1999). Tropical perennial forests are among the least represented in Costa Rica’s protected areas system (Stiles, 1985), although there are large reserves in southern Nicaragua and eastern Panama. Most wetland forests in the lowlands are too small and isolated to sustain viable populations of powerful species; the only one connected with tall forests is La Selva in Costa Rica (just over 1,700 ha), which is too small to protect much of the avifauna (Boza 1996 and pers comm, Stiles and Skutch 1989) and other larger taxa. Only about 130,000 ha in the Atlantic zone of the lowlands are currently protected and difficult economic conditions offer little likelihood that the area under protection will be significantly expanded (Powell et al. 1992).
The lack of protection of the Caribbean lowlands and the strong bias towards deforestation at elevations below 1,000 m above sea level (Powell et al 1992) contribute to the fragmentation and elimination of these forests. With gradual slopes and relatively good access, much of the remaining hillside forest in Costa Rica has been intervened or exists in small fragments.
Types And Gravity Of Threats
Flat areas with alluvial soils are found in banana cultivation, while less fertile basalt soils have been cut more recently and converted into cattle pastures. The last remaining intact forests in this ecoregion are currently under tremendous logging pressure and are being cleared quickly (proambiente 1998). In some cases, unregulated destruction is occurring, despite current legislation to protect forests. The clearings have even been made illegally within many parks-including the Tortuguero National Park-that now provides access to poachers.
The Mesoamerican biological corridor, which aims to improve the connectivity between the habitats of the Atlantic slope, can provide some necessary support for new or expanded protected areas or for payments for environmental services provided by private lands.